Both Uses

principal
in
Goodbye Stranger
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The three audition judges were stationed just below the stage: the vice principal, Mr. Ramos; the head of the language department, Madame Lawrence; and Mr. Partridge, who stood at the light board, which he'd rolled out on its metal cart.†
p. 142.4 *

principal = most important; or person that is most important
He's the vice principal.†
p. 155.1

Definitions:

(1) (principal)
most important; or person who is most important
The exact meaning of principal can depend upon its context. For example:
- "the principal idea" or "the principal performer" -- the most important
- "the principal of the school" -- the person in charge
- "a principal of a company" -- an owner or person with controlling authority
- "the principal in a transaction" (as contrasted to the agent) -- the person on whose behalf an agent acts
(2) (meaning too rare to warrant focus)
See a comprehensive dictionary for specialized senses in finance, architecture, law, chemistry, and music.